While the use of polycarbonate in the field of the safety eyewear market has been established, its use for molding of certain opthalmic vision care products which also protect against UV radiation has been limited. Existing polycarbonate products are satisfactory for applications where moderate UV screening is required, i.e. up to about 380 NM (nanometers) cutoff. Recent information indicates that radiation between 274 NM and 400 NM may be damaging to the eye and studies point to that UV radiation is a cause of cataracts. The current standards respecting opthalmic lenses include requirements of 0% transmission at 390 NM, 0 to 8% transmission at 395 NM and 0.1 to 15%Z transmission at 400 NM. For safety goggle lenses the standards require 0% transmission at 400 NM.
The art recognizes the need to improve the UV stability of polycarbonate resins and to minimize the transmission of harmful UV radiation through polycarbonate molded parts. While UV absorbers are generally known, not all are compatible with polycarbonate resins at the high temperature required for moldings. Representative of the art in this connection is U.S. Pat. No. 4,096,115 which discloses a large number of UV stabilizers said to be effective in any of a great number of polymeric compositions.
The relevant art is noted to include U.S. Pat. No. 3,322,719 which discloses polycarbonates made stable in respect to UV radiation upon the incorporation therewith of a co-stabilizer selected from a group which includes phosphoric acids, boric acid, and certain phosphates and any member selected among certain benzophenones and a certain 2-(2'-hydroxy-5'-tertiary octylphenyl)-benzotriazole (Cyasorb.RTM.5411). Also relevant in this context is U.S. Pat. No. 3,367,958 which discloses UV stabilized polycarbonates containing up to 0.5% of 2-(2'-hydroxy-5'-methylphenyl)-benzotriazole.
U.S. Pat. No. 3,502,613 is noted to disclose polypropylene compositions which are made UV stable by the incorporation of the stabilizer of the present invention as a co-additive. Also, U.S. Pat. No. 3,892,889 discloses the UV stabilization of polycarbonate by treating the surface of the molded articles with a liquid mixture containing UV absorbers. The absorbers encompass within their scope the stabilizer of the present invention. U.S. Pat. No. 4,206,111 discloses that certain benzotriazoles--including stabilizers of the present invention--are made more efficient as stabilizers of polyolefins upon the addition to the compositions of certain diphosphonites and an oxidation inhibitor. U.S. Pat. No. 4,283,327 discloses UV stabilizers, including certain benzotriazoles which are effective in the context of polycarbonate compositions.